Canadian publisher
Bev Editions has most of its backlist free.
LGBTQA publisher
NineStar Press has most of its backlist on sale.
Speculative fiction / gay interest publisher
Lethe Press has most of its backlist on sale or free. Notable anthology series with mostly discounted volumes:
Heiresses of Russ: The Year's Best Lesbian Speculative Fiction, with
Heiresses of Russ 2016 free
Wilde Stories: The Year’s Best Gay Speculative Fiction
Best Gay Stories, with
Best Gay Stories 2015 free